Why Won't My Dog or Cat's Diabetes Stabilise? Common Causes
If your pet's diabetes isn't responding to treatment, there are usually specific, identifiable reasons. What commonly causes poor control, and what to ask your vet.
Why won't my dog or cat's diabetes stabilise?
Quick answer
If your pet's diabetes isn't stabilising despite consistent insulin and feeding, there is usually a specific, identifiable reason — most often insulin handling problems, a hidden urinary tract infection, or in some cases another hormonal condition such as Cushing's disease in dogs or acromegaly in cats. This is worth raising with your vet rather than assuming the treatment simply isn't working.
Species: Dogs and cats
Key takeaways
- Poor control has several possible explanations, and this guide cannot identify which one applies to your pet.
- Insulin storage, preparation and injection technique are practical things to review with your vet first.
- Hidden infections and hormonal conditions can affect insulin resistance without obvious symptoms.
- Never change insulin, doses or treatment timing without your veterinary team's instructions.
Insulin handling problems (check this first)
Insulin can lose effectiveness if it has been shaken instead of gently rolled, left unrefrigerated for too long, frozen, or used past its expiry. A technique issue with the injection can also mean the intended dose does not reach the right place. These details are worth checking calmly with your vet or veterinary nurse.
For practical background, see insulin storage and travel and how to give an insulin injection. Do not use either guide to change your pet's treatment plan without veterinary advice.
A hidden urinary tract infection
Urinary tract infections are common in diabetic pets and can genuinely contribute to insulin resistance. The important, slightly unsettling fact is that they can be occult: present without obvious signs and even with a normal-looking urine test. That is why your vet may recommend a urine culture even if your pet seems otherwise well.
This is one of the more fixable causes of poor control once it is found. Whether testing is appropriate is a veterinary decision.
Cushing's disease (dogs)
Cushing's disease, or hyperadrenocorticism, means the body is producing too much of its own steroid hormone. Steroid hormones can make insulin less effective, making Cushing's disease one of the common causes of insulin resistance in diabetic dogs alongside obesity.
In an unspayed female dog, diestrus — the hormonal phase after a season — can also affect insulin resistance. Specific blood tests are used to investigate these possibilities. Raise changes or concerns with your vet rather than trying to interpret hormone signs at home.
Acromegaly (cats)
Acromegaly is a growth hormone disorder, usually caused by a small pituitary tumour. Research has found IGF-1 levels suggestive of acromegaly in around a quarter of a large cohort of diabetic cats, although most diabetic cats do not have this condition.
A cat may need unusually high insulin doses despite a consistent routine. Some owners notice physical changes such as a broadening face or louder breathing or snoring, which can otherwise be put down to ageing. These signs are not diagnostic. An IGF-1 blood test is one way a vet may investigate it, and confirmed cases have treatment options. A specialist should guide decisions.
Read more in feline acromegaly and diabetes.
Obesity
Excess weight is one of the most common and directly modifiable contributors to insulin resistance in both species. Weight management is something you and your vet can work on together, with a plan that protects nutrition and avoids unsafe rapid changes.
See the relevant guides for feeding a diabetic dog and feeding a diabetic cat.
What to bring to this conversation with your vet
Bring or record:
- your Mello log of doses and readings
- how you store, prepare and mix the insulin
- any recent changes in appetite, thirst, weight or energy
- any vomiting, diarrhoea or urinary changes
- for a female dog, whether she is spayed and the date of her last season
- a list of all medicines, supplements and recent veterinary tests
Your vet can decide which information matters most and whether further tests are appropriate. Do not use this checklist to diagnose a condition or alter insulin yourself.
Frequently asked questions
Why won't my pet's diabetes stabilise?
There are several possible explanations, including handling or injection problems, infection, hormonal disease and obesity. A vet needs to assess the pattern rather than assuming the insulin itself has failed.
Can a hidden infection affect my pet's blood sugar?
Yes. An occult urinary infection may have no obvious signs, so your vet may suggest a urine culture even when a basic urine test looks normal.
What is Cushing's disease and how does it relate to diabetes?
It is a condition in which the body produces too much of its own steroid hormone. That can make insulin less effective, particularly in dogs.
What is acromegaly in cats?
It is a growth hormone disorder, usually linked to a small pituitary tumour, that can make diabetes difficult to stabilise. Your vet may discuss an IGF-1 blood test.
Should my dog be spayed if she's diabetic?
The hormonal cycle can affect insulin resistance in an unspayed female dog, but spaying is an individual decision to make with your vet.
How long should I give a new insulin regime before assuming it isn't working?
Do not make that decision or change treatment alone. Follow the review plan your vet gives you and contact them sooner if your pet becomes unwell.
Sources and further reading
- AAHA Diabetes Management Guidelines for Dogs and Cats — troubleshooting section.
- Niessen SJM et al. “Feline acromegaly: an essential differential diagnosis for the difficult diabetic.” Journal of Feline Medicine and Surgery.
- Behrend EN. “Cushing's Syndrome and Other Causes of Insulin Resistance in Dogs.” Veterinary Clinics: Small Animal Practice.
- Peterson ME et al. Studies of bacterial cystitis incidence in diabetic dogs and cats.
- Home glucose monitoring
- Feline acromegaly and diabetes
- Mello FAQ
This guide is for general education, not diagnosis or treatment. Do not change insulin or any other treatment without your vet's instructions.
Use Mello to keep a clear record for your veterinary team.
Last updated: 9 August 2026
Reviewed by: Mello Editorial Team
Mello helps diabetic pet owners track routines, spot patterns and share clearer updates with their veterinary team.
When to contact your vet
- Contact your vet promptly if your pet’s symptoms, appetite, drinking, urination, behaviour or glucose readings change unexpectedly.
- Ask your vet for advice before changing insulin, food, exercise or any other part of your pet’s routine.
- Seek urgent veterinary care for collapse, seizures, severe weakness, repeated vomiting, or suspected hypoglycaemia or diabetic ketoacidosis.
Quick answers
What's Next?
Continue your diabetes management journey with these recommended next steps.
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Home Glucose Monitoring for Pets
How to monitor your diabetic dog's or cat's blood glucose at home — glucometer selection, testing techniques, building a diabetic pet glucose log, and why home readings beat clinic readings.
Diabetic Pet Life Expectancy: Prognosis & Quality of Life
What's the prognosis for diabetic dogs and cats? Learn about life expectancy, quality of life, and factors affecting longevity.
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